In the art of pilot operated fluid or liquid control valves such as disclosed, for example, in U.S. Pat. Nos. 3,593,957, 3,768,507 and 3,872,878, it is common to use a solenoid actuated armature or plunger for controlling the flow of liquid through a vent opening within the center of a flexible diaphragm valve member. This control of the vent opening controls the movement of the diaphragm valve member by means of differential hydraulic pressure across the valve member and thereby controls the flow of fluid through the valve.
U.S. Pat. Nos. 3,873,059 and 3,955,791, which issued to Applicant, disclose means for controlling the flow of liquid through the vent passage within the diaphragm valve member by controlling movement of the plunger in response to actuation of an elongated U-shaped bimetal element. The element is adapted to be connected as a resistance in series with an electrical load such as a motor. The pilot operated fluid control valve disclosed in Applicant's patents provides the primary advantage of reducing the production or manufacturing cost of the valve, but presents certain problems or disadvantages. For example, the pivotal pin used to move the valve plunger in response to movement of the bimetal actuating element requires a flexible pivotal seal element which is exposed to the liquid or water supply pressure. Such an exposure provides the possibility of a liquid leak from the high pressure side.
As mentioned above, the bimetal actuating element disclosed in Applicant's patents requires that the element be connected in series with another electrical load such as a motor or water heating element. Thus the bimetal actuating element cannot be connected directly to a conventional 110 volt power supply, for example, from an automatic control timer. The movement of the bimetal actuating element is also relatively slow which requires energizing the bimetal actuating element in advance of the time when it is desired for the valve to open and to de-energize the actuating element in advance of the time when it is desired for the valve to close. While it is possible to heat the bimetal actuating element by means of an electrical resistance heating coil surrounding the element, for example, as dissclosed in U.S. Pat. No. 3,643,913, so that the valve may be operated directly from a 110 volt power source, the addition of such a heating coil increases the cost of the valve assembly.